Electrodes have been used to stimulate contraction of the heart or to reverse certain life threatening arrhythmias, where electrical energy is applied to the heart via the electrodes to return the heart to normal rhythm. Electrodes have also been used to sense and deliver pacing pulses to the atrium and ventricle. Cardiac pacing may be performed by a transvenous method or by electrodes implanted directly onto the epicardium. For transvenous pacing systems, a lead having an electrode is positioned in the right ventricle and/or in the right atrium through a subclavian vein, and the proximal electrode terminals are attached to a pacemaker which is implanted subcutaneously.
Some lead designs have “floating” electrodes or electrodes which are not attached to the endocardial wall of the heart. The floating electrodes lay in the blood pool or against the endocardial wall of the heart and the electrode may move slightly within the heart. Since the location of floating electrodes is not fixed with respect to the endocardial wall, the electrical performance of these electrodes varies and is generally less than optimal. Both the electrical sensing capability as well as the pacing delivery capability of such electrodes are suboptimal. The pacing parameters of such a floating electrode are also suboptimal. In addition, the floating electrodes can require increased voltage which unnecessarily drains the battery.
As an alternative to floating electrodes, leads have been provided with passive fixation elements that affix the electrode to the endocardial wall over time. With passive fixation elements, it can be difficult to determine whether the lead will affix in the location at which it is implanted. Active fixation elements, such as a helix, have also been provided with distal ends of leads which allow a lead to be affixed to the endocardial wall. The helix is rotated to screw the lead into the endocardial wall. To rotate the helix toward and into the endocardial wall, a stylet is disposed within the lead and rotated. As the stylet is rotated however, the active fixation element may jump out of the end of the lead and damage tissue, and/or the helix. In addition, it is difficult for the implanter to determine how many turns to the stylet is necessary to advance the helix a certain distance.
A cardiac pacing system typically includes a pulse generator which supplies the electrical energy to the lead. The pulse generator may be implanted into a subcutaneous pocket made in the wall of the chest. A lead coupled with the pulse generator is routed subcutaneously from the pocket to the shoulder or neck where the lead enters a major vein, such as the subclavian vein, and into the heart. The proximal end of the lead is coupled both electrically and mechanically with the pulse generator at A distal end of the lead is placed within the heart, and a proximal end is placed within a pacemaker.
When leads with multiple conductors are involved, the conductors are individually and electrically coupled with the pulse generator at a proximal end of the multiple conductors. The multiple conductors at the proximal end are electrically insulated from each other to prevent shorts and limit electrical leakage between conductors. Medical adhesive is used to insulate the multiple conductors at the proximal end of the lead. However, the process of using medical adhesive is timely and costly to assemble. In addition, the medical adhesive bonds inconsistently, sometimes resulting in mechanical and electrical separation between the components.
The proximal end of the lead includes a terminal connection which provides the electrical and mechanical connection between the pacemaker and the proximal end of the lead. When inserted into the pacemaker, the components of the terminal connection undergoes axial stress as the implanter forces the proximal end of the lead into the pacemaker. After inserted, the implanter may pull on the lead to ensure the terminal end is sufficiently seated in the pacemaker, placing additional axial stress on the terminal connection.
Accordingly, there is a need for a lead with multiple conductors which are reliably insulated from one another. What is further needed is a lead having a terminal connection which can accommodate axial stress placed thereon.